string Substr(string a1, string a2)
{
			string res;
			int l = MakeEqLength(a1,a2);
			res = a1;
            int i;
			string temp1;
            int temp;
            int tran = 0;
            int count = 0;
            bool flag = false;
            for (i = 0; i < l; i++)
            {
                temp = ((a1[i]-'0') - (a2[i]-'0'));
                if (temp < 0)
                {
					temp1=a1;
					a1=a2;
					a2=temp1;
					flag = true;
                    break;
                }
                else if (temp > 0)
                    break;
                else if (temp == 0)
                    continue;
            }
                for (i = l - 1; i >= 0; i--)
                {
                    temp = ((a1[i]-'0') - (a2[i]-'0')) - tran;
                    if (temp < 0)
                    {
                        tran = 1;
                        res[i]=temp+10+48;
                    }
                    else
                    {
                        tran = 0;
                        res[i]=temp+48;
                    }
                }
           while (res[0] == '0' && res.length() != 1) // erase leading zeros
			res.erase(0, 1);
            if (flag == true)
            {
                cout << "-";
            }
            return res;
            /*string res;
			int l = MakeEqLength(a1,a2);
			res = a1;
            int i;
            int temp;
            int tran = 0;
            int count = 0;
            bool flag = false;
            for (i = 0; i < l; i++)
            {
                temp = ((a1[i]-'0') - (a2[i]-'0'));
                if (temp < 0)
                {
                    flag = true;
                    break;
                }
                else if (temp > 0)
                    break;
                else if (temp == 0)
                    continue;
            }
            if (flag == true)
            {
                for (i = l - 1; i >= 0; i--)
                {
                    temp = ((a2[i]-'0') - (a1[i]-'0')) - tran;
                    if (temp < 0)
                    {
                        tran = 1;
                        res[i]=temp+10+48;
                    }
                    else
                    {
                        tran = 0;
                        res[i]=temp+48;
                    }
                }
            }
            else
            {
                for (i = l - 1; i >= 0; i--)
                {
                    temp = ((a1[i]-'0') - (a2[i]-'0')) - tran;
                    if (temp < 0)
                    {
                        tran = 1;
                        res[i]=temp+10+48;
                    }
                    else
                    {
                        tran = 0;
                        res[i]=temp+48;
                    }
                }
            }
           while (res[0] == '0' && res.length() != 1) // erase leading zeros
			res.erase(0, 1);
            if (flag == true)
            {
                cout << "-";
            }
            return res;*/
}